Diffuse Galactic Gamma Rays from Shock-Accelerated Cosmic Rays

TL;DR

This paper models gamma-ray emissions from the galaxy using shock-accelerated cosmic rays with a specific power-law spectrum, fitting observational data and clarifying spectral features.

Contribution

It introduces a theoretical model of cosmic-ray acceleration leading to gamma-ray spectra that match Fermi-LAT observations, explaining spectral breaks.

Findings

Cosmic-ray flux follows a p^-s spectrum with s ~ 2.8.

The model fits gamma-ray spectra of high-latitude and molecular clouds.

Spectral breaks are explained by the energy-based description of cosmic-ray flux.

Abstract

A shock-accelerated particle flux \propto p^-s, where p is the particle momentum, follows from simple theoretical considerations of cosmic-ray acceleration at nonrelativistic shocks followed by rigidity-dependent escape into the Galactic halo. A flux of shock-accelerated cosmic-ray protons with s ~ 2.8 provides an adequate fit to the Fermi-LAT gamma-ray emission spectra of high-latitude and molecular cloud gas when uncertainties in nuclear production models are considered. A break in the spectrum of cosmic-ray protons claimed by Neronov, Semikoz, & Taylor (PRL, 108, 051105, 2012) when fitting the gamma-ray spectra of high-latitude molecular clouds is a consequence of using a cosmic-ray proton flux described by a power law in kinetic energy.